A comparison will be made of three levels of enamel in relation to ultrastructure and solubility properties. Enamel near the dentinoenamel junction, the mid-region of normal enamel and the surface enamel will be examined. The peripheral crystals of the enamel prism which are sometimes more acid resistant will be focused on at the three levels. Also, variations in this peripheral region will be examined in regard to deciduous versus permanent enamel and newly erupted versus teeth with long exposure to the oral environment. Microradiographic and transmission electron microscopic studies of incipient caries in proximal and fissure areas will be carried out. The role of shortening of the long axis of the crystals in the accentuation of cross-striations and Retzius lines will be examined. Changes in crystals at the front of the incipient lesion as well as crystals in the resistant surface layer will be studied. Remineralization experiments will include "en bloc" treatment of partially demineralized enamel. Ca/P solutions with and without flouride will be used. Conditions in which the dissolved centers of the crystals reform is the desired goal.